From: Mickaël Salaün <redacted>

Create and use the access_mask_t typedef to enforce a consistent access
mask size and uniformly use a 16-bits type.  This will helps transition
to a 32-bits value one day.

Add a build check to make sure all (filesystem) access rights fit in.
This will be extended with a following commit.

Signed-off-by: Mickaël Salaün <redacted>
Link: https://lore.kernel.org/r/20220221212522.320243-2-mic@digikod.net (local)
---
 security/landlock/fs.c      | 19 ++++++++++---------
 security/landlock/fs.h      |  2 +-
 security/landlock/limits.h  |  2 ++
 security/landlock/ruleset.c |  6 ++++--
 security/landlock/ruleset.h | 17 +++++++++++++----
 5 files changed, 30 insertions(+), 16 deletions(-)

diff --git a/security/landlock/fs.c b/security/landlock/fs.c
index 97b8e421f617..9de2a460a762 100644
--- a/security/landlock/fs.c
+++ b/security/landlock/fs.c

@@ -150,7 +150,7 @@ static struct landlock_object *get_inode_object(struct inode *const inode)
  * @path: Should have been checked by get_path_from_fd().
  */
 int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
-               const struct path *const path, u32 access_rights)
+               const struct path *const path, access_mask_t access_rights)
 {
        int err;
        struct landlock_object *object;

@@ -182,8 +182,8 @@ int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,

 static inline u64 unmask_layers(
                const struct landlock_ruleset *const domain,
-               const struct path *const path, const u32 access_request,
-               u64 layer_mask)
+               const struct path *const path,
+               const access_mask_t access_request, u64 layer_mask)
 {
        const struct landlock_rule *rule;
        const struct inode *inode;

@@ -223,7 +223,8 @@ static inline u64 unmask_layers(
 }

 static int check_access_path(const struct landlock_ruleset *const domain,
-               const struct path *const path, u32 access_request)
+               const struct path *const path,
+               const access_mask_t access_request)
 {
        bool allowed = false;
        struct path walker_path;

@@ -308,7 +309,7 @@ static int check_access_path(const struct landlock_ruleset *const domain,
 }

 static inline int current_check_access_path(const struct path *const path,
-               const u32 access_request)
+               const access_mask_t access_request)
 {
        const struct landlock_ruleset *const dom =
                landlock_get_current_domain();

@@ -511,7 +512,7 @@ static int hook_sb_pivotroot(const struct path *const old_path,

 /* Path hooks */

-static inline u32 get_mode_access(const umode_t mode)
+static inline access_mask_t get_mode_access(const umode_t mode)
 {
        switch (mode & S_IFMT) {
        case S_IFLNK:

@@ -563,7 +564,7 @@ static int hook_path_link(struct dentry *const old_dentry,
                        get_mode_access(d_backing_inode(old_dentry)->i_mode));
 }

-static inline u32 maybe_remove(const struct dentry *const dentry)
+static inline access_mask_t maybe_remove(const struct dentry *const dentry)
 {
        if (d_is_negative(dentry))
                return 0;

@@ -631,9 +632,9 @@ static int hook_path_rmdir(const struct path *const dir,

 /* File hooks */

-static inline u32 get_file_access(const struct file *const file)
+static inline access_mask_t get_file_access(const struct file *const file)
 {
-       u32 access = 0;
+       access_mask_t access = 0;

        if (file->f_mode & FMODE_READ) {
                /* A directory can only be opened in read mode. */

diff --git a/security/landlock/fs.h b/security/landlock/fs.h
index 187284b421c9..74be312aad96 100644
--- a/security/landlock/fs.h
+++ b/security/landlock/fs.h

@@ -65,6 +65,6 @@ static inline struct landlock_superblock_security *landlock_superblock(
 __init void landlock_add_fs_hooks(void);

 int landlock_append_fs_rule(struct landlock_ruleset *const ruleset,
-               const struct path *const path, u32 access_hierarchy);
+               const struct path *const path, access_mask_t access_hierarchy);

 #endif /* _SECURITY_LANDLOCK_FS_H */

diff --git a/security/landlock/limits.h b/security/landlock/limits.h
index 2a0a1095ee27..458d1de32ed5 100644
--- a/security/landlock/limits.h
+++ b/security/landlock/limits.h

@@ -9,6 +9,7 @@
 #ifndef _SECURITY_LANDLOCK_LIMITS_H
 #define _SECURITY_LANDLOCK_LIMITS_H

+#include <linux/bitops.h>
 #include <linux/limits.h>
 #include <uapi/linux/landlock.h>

@@ -17,5 +18,6 @@

 #define LANDLOCK_LAST_ACCESS_FS                LANDLOCK_ACCESS_FS_MAKE_SYM
 #define LANDLOCK_MASK_ACCESS_FS                ((LANDLOCK_LAST_ACCESS_FS << 1) - 1)
+#define LANDLOCK_NUM_ACCESS_FS         __const_hweight64(LANDLOCK_MASK_ACCESS_FS)

diff --git a/security/landlock/ruleset.h b/security/landlock/ruleset.h
index 2d3ed7ec5a0a..7e7cac68e443 100644
--- a/security/landlock/ruleset.h
+++ b/security/landlock/ruleset.h

@@ -9,13 +9,20 @@
 #ifndef _SECURITY_LANDLOCK_RULESET_H
 #define _SECURITY_LANDLOCK_RULESET_H

+#include <linux/bitops.h>
+#include <linux/build_bug.h>
 #include <linux/mutex.h>
 #include <linux/rbtree.h>
 #include <linux/refcount.h>
 #include <linux/workqueue.h>

+#include "limits.h"
 #include "object.h"

+typedef u16 access_mask_t;
+/* Makes sure all filesystem access rights can be stored. */
+static_assert(BITS_PER_TYPE(access_mask_t) >= LANDLOCK_NUM_ACCESS_FS);